Suction-operated device for feeding sheets one by one to a point of utilization

ABSTRACT

A SUCTION-OPERATED DEVICE FOR LIFTING SHEETS ONE BY ONE FROM A STACK OF SHEETS AND FEEDING THE SAME TO A POINT OF UTILIZATION COMPRISES AN UPRIGHT CYLINDER IN WHICH A PISTON MOUNTING A SUCTION HEAD IS SEQUENTIALLY LOWERED FROM A POSITION ABOVE THE UPPERMOST SHEET ON THE STACK INTO A POSITION SUCKING ON AND HOLDING THIS SHEET AND LIFTED FROM THIS POSITION INTO A POSITION IN WHICH THE HELD SHEET IS READY FOR CONVEYANCE TO THE POINT OF UTILIZATION. THESE MOVEMENTS OF THE SUCTION HEAD ARE CONTROLLED BY CREATING TEMPORARY PRESSURE DIFFERENTIALS IN THE CYLINDER CAUSING THE AFOREDESCRIBED DOWN AND UP MOVEMENTS OF THE SUCTION HEAD. UPON ARRIVAL OF A SUCKED ON AND HELD SHEET AT THE POINT OF UTILIZATION, THE SHEET IS RELEASED BY DISCONTINUING THE VACUUM IN THE CYLINDER. THE DEVICE FURTHER PERMITS ADJUSTMENT OF THE LENGTH OF THE STROKE PERFORMED BY THE PISTON DURING EACH OPERATION.

Nov. 14, 1972 A. SCHWEBEL 3,7025698 SHEETS ONE BY ONE TO A POINT OF UTILIZATION SUCTION-OPERATED DEVICE FOR FEEDING Filed July 2, 1971 FIG.

INVENTOR.

ADOLF SCHWEBEL. BYH

Afro/wens FIG. 4

3,702,698 SUCTION-OPERATED DEVICE FOR FEEDING SHEETS ONE BY ONE TO A POINT OF UTILIZATION Adolf Schwebel, Offenbach am Main, Germany, assignor to Mabeg-Maschinenbau G.m.b.H. Nachf. Hense & Pleines G.m.b.H. & Co., Offenbach am Main, Germany Cl Filed July 2]; 1971, No. 1513,3161 16 1970 aims priority, app cation rmany, y

P 20 35 294.7 It. Cl. B6511 3/08 US. Cl. 271-26 3 Claims ABSTRACT OF THE DISCLOSURE A suction-operated device for lifting sheets one by one from a stack of sheets and feeding the same to a point of utilization comprises an upright cylinder in which a piston mounting a suction head is sequentially lowered from a position above the uppermost sheet on the stack into a position sucking on and holding this sheet and lifted from this position into a position in which the held sheet is ready for conveyance to the point of utilization. These movements of the suction head are controlled by creating temporary pressure differentials in the cylinder causing the aforedescribed down and up movements of the suction head. Upon arrival of a sucked on and held sheet at the point of utilization, the sheet is released by discontinuing the vacuum in the cylinder. The device further permits adjustment of the length of the stroke performed by the piston during each operation.

The invention relates to a device for picking up sheets one by one for feeding the same to a point of utilization such as the locating stops on the feed table of a printing press or other sheet processing machine and more particularly to a sheet feeding device in which pick-up and holding of the sheets are effected by a suction head controlled by the position of a piston in a cylinder.

BACKGROUND OF THE INVENTION There are known various types of suction-operated sheet feeding devices of the general kind above referred to in which a piston and a piston rod mounting the suction head are guided by means of several compartments in a cylinder. Devices of this type as now known, require complex, expensive and operationally not reliable mechanical control means. Moreover, they operate slowly and sluggishly and are hence not satisfactory for high output sheet processing machines.

Modern technology in the industry here involved, demands more rapid processing of sheets per unit of time than sheet feeding devices the sheet pick-up assembly of which is arranged in the heretofore conventional manner are capable of performing.

THE INVENTION It is a broad object of the invention to provide a novel and improved suction-operated sheet feeding device which is simple in construction, requires little servicing and is capable of feeding sheets, one by one, at the extremely high speeds now demanded in the industry.

A more specific object of the invention is to provide a novel and improved sheet feeding device of the general kind above referred to in which the distance which the suction head of the device must travel during each operation or in other words, the stroke of the piston which controls the up and down movements of the suction head can be conveniently adjusted.

United States Patent O 3,702,698 Patented Nov. 14, 1972 Still another object of the invention is to provide a novel and improved sheet feeding device of the general kind above referred to in which the piston and with it the suction head supported by the piston is lifted in several stages thereby greatly simplifying the construction and the operation of the device.

SUMMARY OF THE INVENTION The aforepointed out objects, features and advantages of the invention and other objects, features and advantages which will be pointed out hereinafter are obtained by providing an upright cylinder which is open at its top and closed at its bottom. A bushing is fixedly mounted in the cylinder intermediate the length thereof and a first and a second piston are slidable in the cylinder spaces above and below the bushing respectively. The suction head of the device is mounted at the end of a tube which slidably extends from the second piston below the bushing through the bottom of the cylinder. This suction head communicates through the tube with the cylinder space between the second piston and the bottom of the cylinder. A compression spring in the cylinder space between the cylinder bottom and the second piston biases said piston toward abutment with the bushing. A conduit is connected to this cylinder space for evacuating the same.

A stop member preferably extends from the first piston through the bushing to coact With the second piston for controlling the stroke length thereof by adjusting the effective length of the stop member and thus the length of the stroke.

The bushing includes a duct connecting the cylinder spaces above and below the bushing and the second piston includes a duct connecting the cylinder spaces above and below this piston. The top side of the first piston is open to the atmosphere. The effective cross-sections of the ducts in the bushing, the pistons and the opening of the suction head are so correlated that vacuum generated in the cylinder space between the second piston and the cylinder bottom is effective for first moving the first piston into a position abutting against the bushing due to atmospheric pressure acting upon the top side of this piston, then moving the second piston against the action of a compression spring into a lower limit position in which the suction head attracts and holds the uppermost sheet on a stack of sheets and finally lifts the suction head together with the sheet for conveyance to a point of utilization. Discontinuation of the vacuum releases the held sheet and causes the spring to return the second piston supporting the suction head and also the first piston to the initial or rest position.

DETAILED DESCRIPTION OF THE INVENTION In the accompanying drawing a preferred embodiment of the invention is shown by way of illustration and not by Way of limitation.

In the drawing:

FIG. 1 is an elevational sectional view of the suctionoperated sheet feeding device in its rest position;

FIG. 2 is a similar sectional view showing an initial stage of the movement of the device toward its sheet pick-up position;

FIG. 3 is a sectional view similar to FIGS. 1 and 2 and showing the device in a further advanced position toward its sheet pick-up position;

FIG. 4 is a sectional view similar to the previous figures and showing the device at the moment of the pick-up of a sheet; and

FIG. 5 is a sectional view similar to the previous figures and showing the device after pick-up of the sheet and ready for delivering the picked-up sheet to a point of utilization.

Referring now to the figures more in detail and first to FIG. 1 the device according to the invention as exemplified in this figure comprises an upright cylinder 1 closed at its bottom and open at its top via an opening 30. A bushing or collar 16 is fixedly mounted intermediate the length of the cylinder. A sealing ring 16a is preferably placed upon the top side of the bushing. A first piston 24 is slidable in the cylinder above bushing 16 and a second piston 4 is slidable in the cylinder below the bushing.

Piston 24 mounts a stop member comprising a threaded portion 27 threaded through the piston and a smooth portion 26 slidably extended through an axial bore of bushing 16. The smooth member portion preferably terminates in a set-off part 26a. The total length of the stop member is such that when piston 24 is positioned in abutment with bushing 16 (see for instance FIG. 2) the smooth portion 26 protrudes from the bottom side of the bushing for a purpose which will be more fully explained hereinafter. The length of the protruding portion, which is the eifective length of the stop member, may be selectively adjusted by screwing member portion 27 more or less deeply into piston 24. A lock nut 27a may be provided to secure the stop member in its adjusted position.

Piston 4 has secured thereto or integral therewith a tube 3. This tube is slidably extended through the bottom wall of the cylinder and mounts at its end protruding from the bottom wall a suction head 6. The downwardly facing side 6a of this head communicates with the space 13 in tube 3 through one or more ducts, three ducts 10, 11 and 12 being shown. A sealing or cushioning ring 7 is preferably provided at the upper rim of the same to cushion the impact of the head against the cylinder during the operation of the device to be described hereinafter. Space 13 communicates with cylinder space 8 between piston 4 and cylinder bottom through one or more ports 9 in any position of the piston within the cylinder the cyling 16 includes one or more ducts 19 connecting the cylinder space above the bushing with the cylinder space below the bushing. Similarly, piston 4 includes one or more ducts connecting the cylinder spaces above and below the piston. A compression spring within space 8 and preferably encompassing tube 3 biases piston 4 toward the position of FIG. 1 in which the piston abuts against the bushing and suction head 6 occupies the position of FIG. 1.

Piston 4 is movable from the position of FIG. 1 into a lower limit position (see FIG. 4). As may be noted, due to the space occupield by spring 15 space 8 is present in any position of piston 4 through its volume changes depending upon the location of the piston in the cylinder. Space 8 communicates with a conduit 22 which should be visualized as being selectively connectable to a supply of suction or to the atmosphere.

As previously described, the device of the invention serves to pick up sheets 31, one by one, from a stack 2 of sheets diagrammatically indicated in FIGS. 4 and 5. This stack should be visualized as resting on a stack table conventional for printing presses and other sheet processing machines, that is, a table which is gradually lifted as the stack is depleted so that the top sheet is always at substantially the same level.

It should further be visualized that the device after having picked up a sheet (see FIG. 5) is conveyed to a point of utilization such as the feed table of a printing press and returned for the pick-up of another sheet. Conveying assemblies of this kind are well known in the art, they are not shown or described in detail as they do not constitute part of the invention and are not essential for the understanding of the invention.

The Operation of the sheet feeding device as hereinbefore described is as follows: I

FIG. 1 shows the device in its inactive or rest position. All the aforedescribed components which are slidable within cylinder 1 occupy the illustrated positions due to the action of spring 15. As isalso shown, there are formed a cylinder space 23 above piston 24, a cylinder space 21 between piston 24 and bushing 16 and cylinder space 8 between piston 4 and the bottom of the cylinder. All the three cylinder spaces are at atmospheric pressure via the ducts in the suction head, the interconnecting ducts in the piston 4 and the bushing, conduit 22 and opening 30.

Let it now be assumed that it is desired to operate the device for picking up and holding a sheet 31 as it is shown in FIGS. 4 and 5. For this purpose, a sufliciently powerful suction is applied to conduit 22. As a result, a correspondingly hard vacuum is rapidly though temporarily generated in space '8 notwithstanding the continued influx of air through ducts 10, I11 and 12 in the suction nozzle as will be more fully explained hereinafter. The air in space 21, of course will leak out through ducts 19 and 5 into space 8 but not rapidly enough to equalize immediately the pressure in spaces 21 and 8. Accordingly, there exists temporarily the condition that there is a fairly hard vacuum in space 8 and a somewhat reduced atmospheric pressure in space 21. Due to this reduction of pressure, piston 24 the top side of which remains exposed to full atmospheric pressure as space 23 is open to the atmosphere via opening 30, is moved from the position of FIG. 1 into the position of FIG. 2 in which the smooth portion 26 of the stop member protrudes from the bushing thereby depressing piston 4- into the position of FIG. 4. Moreover, space 21 disappears and a new space 20 is formed into which is pressed the remaining air in space 21. As it is evident, the upwardly directed spring force action upon piston 4 is weakened as the upward pressure of the spring is no longer assisted by the atmospheric pressure in space 8 which is under vacuum and thus constitutes a suction space. New space 20 is temporarily still at a pressure higher than the pressure in space 8 as the air in space 20 can only slowly escape through ducts '5, that is, space 20 constitutes a pressure space. The thus temporarily existing pressure differential between spaces 20 and 8 presses piston 4 against the action of spring 15 via the intermediate position of FIG. 3 into the position of FIG. 4. In this position the face 6a of the suction head 6 is in contact with the top sheet 31 or close enough to the same to attract it as it is shown in FIG. 4. In practice, the sheet will usually jump against the head face. Placement of the sheet against the head face will close influx of atmospheric air into space 13 in tube 3 and thus into cylinder space 8 via ports 9. Since the air in space 20 continues to leak through ducts 5 into space 8 connected tosuction conduit 22, the pressure differential between spaces 20 and 8 decays. As a result, spring 15 will snap piston 4 upwardly into the position of FIG. 5 until the piston is stopped by the extension 26a of the stop member. The position of FIG. 5 constitutes the upper limit position of the stroke of piston 4. While piston 24 and thus the stop member are slidable in the cylinder, the spring at this stage of the operation cannot push piston 24 into the position of FIG. 1 due to the atmospheric pressure acting upon the top side of piston 24 and the continuing vacuum in spaces 8 and 20'. As it is shown in FIG. 5, sheet 31 is thus lifted clear of the stack and ready for conveyance to the point of utilization. When this point is reached the suction through conduit 22 is discontinued. As a result, sheet 31 is no longer held by the suction head and spring 15 is now capable of returning pistons 4 and 24 into the position of FIG. 1.

The aforedescribed pressure difierentials temporarily existing between cylinder spaces 8, 20, 21 and 23 are obtained by suitably correlating the cross-sectional areas of the ducts in bushing 16, piston 4 and in suction head 6 and by further suitably selecting the load pressure of spring 15 and the exposed effective areas of the pistons and the bushings. As is readily evident, no fixed ratio can be given for the effective cross-sectional areas of the ducts and the strength of the spring as the necessary dimensions and forces must be specifically calculated for a device of a given size. However, as it is also evident, the necessary calculations will not present any difliculties to any expert in the field as they merely involve very basic and well understood physical requirements. Generally speaking, the ducts 19 should be wider than ducts as it is also shown so that air can rapidly flow from space 21 into space 20 as it is formed but only slowly from space 20 into space '8. The ducts in the suction head should be so narrow that the suction at the head is just sufiieient to hold one sheet.

It should also be pointed out that in actual practice, the aforedescribed sequential stages leading from FIG. 1 to FIG. 5 occur exceedingly rapidly. The sheet feeding device according to the invention as herein described is designed to operate at pick-up speeds of 12,000 to 14,000 per hour. Accordingly, it does not present any problem to obtain required temporary pressure differentials notwithstanding the communications between the spaces involved.

As previously described, the effective length of the stop member controls the upper limit position of piston 4 and thus of the suction head. Accordingly, the level to which sheets are lifted can be conveniently adjusted by varying the effective length of the stop member as previously described. As it is obvious, a change in the stroke length of piston 4 as controlled by its upper limit position also changes correspondingly the period of time required for the completion of a pick-up operation and thus the output obtainable with the device of the invention.

While the invention has been described in detail with respect to a certain now preferred example and embodiment of the invention, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. A device for lifting sheets one by one from a sheet supply and feeding the same to a point of utilization, said device comprisnig in combination:

an upright cylinder open at its top and closed at its bottom;

a bushing fixedly mounted within the cylinder intermediate the length thereof;

a first piston slidable in the cylinder space above said bushing and a second piston slidable in the cylinder space below said bushing;

a tubular member extending from the second piston through the bottom of the cylinder protruding therefrom;

a suction head including a duct mounted on the protruding end of said member, the tubular member communicating with the atmosphere via the duct in the suction head for sucking on and holding a sheet disposed below the head;

a compression spring between the cylinder bottom and the second piston biasing said piston toward abutment with said bushing and limiting a down movement of the second piston to a lower limit position spaced apart from the cylinder bottom to define a suction space within the cylinder in any axial position of the second piston, said tubular member further communicating via a port with said suction space;

a conduit communicating with the suction space in any axial position of the second piston for selectively generating a vacuum in the suction space or admitting air into said space;

a stop member slidably extending from the first piston through said bushing, the axial length of said member being such that it downwardly protrudes from the bushing when the first piston is in a position abutting against the bushing thereby yieldingly stopping the second piston in an upper limit position spaced apart from the bushing for defining a pressure space in the cylinder between the bushing and the second piston,

said bushing including a duct connecting cylinder spaces above and below the bushing, said second piston including a duct connecting cylinder spaces above and below said piston,

the effective cross-sections of the ducts in the bushing, in the piston and in the suction head being so correlated that vacuum generated in the suction space is eflfective for first moving the first piston into the position abutting against the bushing due to the atmospheric pressure continuing to act upon the top side of said piston, said movement of the first piston causing the now protruding stop member to depress the second piston thereby forming a pressure space between the bushing and the second piston, for then moving the second piston against the action of said spring into a lower limit position in which the suction head attracts and holds the sheet therebelow by the suction action of the suction head before air escaping from the pressure space through the duct in the second piston restores pressure equilibrium on both sides of the second piston thereby freeing the spring for moving the second piston into engagement with said stop member, discontinuation of the vacuum in the suction space releasing the held sheet and causing the spring to press the second piston against the protruding portion of the stop member thereby lifting the first piston out of its position of abutment with the bushmg.

2. The device according to claim 1 wherein the effective axial length of the stop member is adjustable for varying the length of the protruding portion of said member when the first piston is in its abutment position and thus the stroke length of the second piston between its upper and lower limit positions.

3. The device according to claim 2 wherein said stop member is a screw bolt threaded through the first piston and having a smooth portion slidably extending through the bushing.

References Cited UNITED STATES PATENTS 2,341,521 2/1944 Baker et al. 271--26 R 2,799,499 7/1957 Perry et al. 27126 R 2,950,913 8/ 1960 Staines 27 l---26 R EVON C. BLUNK, Primary Examiner B. H. STONER, 1a., Assistant Examiner U.S. Cl. X.R. 294-64 R 

